Welding is an area where I have to be careful what I say. I've been called a 'welding snob'.
In a nutshell, the issue with MIG welding is that you really can't see the puddle, so you don't know if you've really tied the two pieces together. You can make a MIG weld that looks beautiful on the surface but you can pull apart with your bare hands.
I am told there are MIG processes that are now acceptable in code work but I have no first hand knowledge of them.
Welding is important enough to deserve a thread of its own.

Last edited by Marty_Knox on Sat Oct 10, 2009 3:30 pm, edited 1 time in total.

King Frey who built boilers for Railroad Supply when Chet Peterson owned it, Migged the boilers together. He also made code boilers for a while, but I do not know if he migged the code boilers, this was back in the Seventies.

But I agree with Marty you should have a pressure vessel welder weld your boiler.

David

We the willing, led by the unknowing, have been doing so much with so little for so long that we are now qualified to do anything with nothing.

Mig welding is accepted by Australian minature boiler code and that is one stringent code ,it does not seem any different to stick or tig if your weld preps and material are correct and you do multi passes when required and a certified code welder ,my Challenger boiler is both tig and mig welded and pressure tested to 300psi and has Australian cert so I'm not sure what the issue is with mig welding?

I come from an engineering/design/mfgr background in the oilfield (read very high pressures / very high temperatures / ZERO failure acceptability.)

I was very interested in this thread when it started, however unfortunately, it seems to have taken an interesting turnout in a different direction.

I think especially from a process / commercial boiler perspective, and from the experiences gathered from 200 years of experience; what we are truely making are not "steam machines" but truly little EXPLOSIVE devices if not constructed correctly, to the wrong specifications, or procedure, and THEN thouroughly tested (Yearly) can main and kill.

It seems to me that there are a lot of folks that are interested / have started / will start to produce miniature boilers without a fundamental understanding of:

A. The requirements for the engineering tasks
B. The materials involved
C. Basic knowledge of the boiler construction

( and not necessarily in that order.)

Can we go back to the fundamentals that this thread started with, I think it was a great start, and I think the insight is needed.

ScaleModeler1974 wrote:Several years ago at the Cabin Fever Expo in York PA I had asked Marty Knox about using mig and or tig welding for boilers and it seamed to me that I was ridiculed for even asking.

The very first weld shop I worked in had built high pressure vessels and heat exchangers and they allways used a root pass with tig then subsequent passes with Fluxed-Core mig.

This is why I ask about mig and tig welding on boilers.

I will admit to a prejudice against MIG welding. Perhaps I do not look at it objectively - I must admit it has come a long way since 1981, when I received my welding training.
As for TIG, I love it! I use it for the root pass often. The extra time it takes to TIG the root is often saved by not having to clean up.

Here is where Marty's divisions should come in, "Up to about 5 1/2 - 6" diameter and 100 PSI copper has many advantages,above that,low carbon steel is the material of choice..."

In my opinion, the two materials, copper or steel, really do need to be treated as two subjects, as the construction is so different.

Were the majority here in the UK, it would be simple as most boilers would be copper, and small. As most are US-based, and many of you on that side of the pond like things large, or larger, then perhaps keeping to steel would be more applicable to the majority.

I think especially from a process / commercial boiler perspective, and from the experiences gathered from 200 years of experience; what we are truely making are not "steam machines" but truly little EXPLOSIVE devices if not constructed correctly, to the wrong specifications, or procedure, and THEN thouroughly tested (Yearly) can main and kill.
Chris

Chris, i have to take some issue with this statement "little EXPLOSIVE devices". we are not covered by the ASME codes because, if below the 5 cu. ft. of volume, our boilers don't explode. they may split open a seam and scald you to death but they don't explode. there has never been an explosion of a miniature boiler that i have ever heard about. i have heard of seams splitting open. i haven't heard of any death related to a miniature boiler accident. i hope it stays that way.